ADR-258: A model hints at the cause of a logged error 

Context 

ADR-044 gave the assistant get_last_exception: an administrator who asks in the chat gets the newest logged error with its stack and source, and the model explains it. Outside the chat nothing did: an administrator on the command line, or one who opens the backend to look at what failed, had the log and no hint. The gap analysis of 2026-09-23 listed "hints for exceptions by AI, for administrators and on the command line" as missing.

Three constraints shape it. The hint must not show anyone more than the person already sees: the log files are readable by whoever runs the CLI and, in the backend, only by administrators. An exception message sits next to secrets (connection strings, tokens; ADR-094 classes it SECRET_ADJACENT), and a provider may be allowed less than that. And a model asked for a cause always names one, so a reader must be able to tell a hint anchored in the stack from a guess.

Decision 

One service, ExceptionHintService, two thin surfaces.

What is sent

The exception class, the message after the sanitizer that masks credentials in URLs, the component, and up to 20 frames as file, line and function name. TYPO3's exception handlers log no trace by default; for their entries LogExceptionReader now takes the class and the throw site from the entry's own exception_class, file and line keys; that class beats one the message quotes. An entry with no class, no frame and a message the provider may not receive is not sent at all. Call arguments are cut from each frame (PHP writes argument values into a trace unless zend.exception_ignore_args is on). No source line is sent; get_last_exception remains the way to read code with a model.

What the provider may receive

The configuration's trust zone decides, through the same ladder the tool loop applies (TrustZoneResolver::ceilingFor()). Class and frames are system diagnostics, the message is secret-adjacent. Below SYSTEM_DIAGNOSTICS no model is asked and the refusal says why; below SECRET_ADJACENT the message is withheld and the hint says it was made without it. With the default zones this means a hint is asked only of a local or privately hosted provider; an operator who wants another one moves that provider's zone, which is the documented switch. A criteria-mode configuration has no provider of its own and counts as external, as it does for the tool loop; name a fixed-model configuration instead.

When a hint is a guess

The model answers with a cause, a next step and the number of the frame the cause sits in. The extension, not the model, labels the hint: it is anchored only when the cited frame exists in the entry's stack and lies in the project's code (inside the project root, not under vendor/, var/ or typo3temp/, which hold generated files, and, in a classic-mode installation, not under typo3/sysext/). Every other hint is shown as a guess.

Surfaces

nrllm:exception:hint (--index, --search, --configuration; default configuration otherwise) prints the entry and the hint. It is not schedulable: a scheduler task would send every logged error out on a timer. The backend module AI > Operation > Error hints is administrator-only and lists the ten newest entries; a hint is asked for per entry by POST, so a page view or a prefetch never sends an error. The form posts a key of the entry, not its position, so an error logged in between is never sent in its place. The hint action checks the administrator again. The module uses the default configuration. The call bypasses the answer cache and is attributed as exception_hint in the usage data.

Not done

No hook in TYPO3's exception handlers. A model call while an exception is rendered would add a provider's latency and an outbound request to every error page, and a failing provider would fail inside the handler.

Consequences 

• An administrator gets a cause and a next step without opening the chat, and can tell an anchored hint from a guess by its heading.
• On an installation whose providers are all external with default zones, both surfaces refuse with the zone named. That is the data-class rule applied, not a defect.
• The failure signature of a regression in the guess rule is a hint shown as anchored whose frame is under vendor/ or missing.